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- # mach: bfin
- // GENERIC CONVOLUTIONAL ENCODER
- // This a generic rate 1/n convolutional encoder. It computes n output
- // bits for each input bit, based on n generic polynomials.
- // It uses the set of BXOR_CC instructions to compute bit XOR
- // reduction from a state masked by a polynomial. For an alternate
- // solution based on assembling several partial words, as in
- // the BDT benchmark, see file conv_enc.c. The solution presented
- // here is slower than conv_enc.c, but more generic.
- //
- // Forward Shift Register
- // -----------------------
- // This solution implements the XOR function by shifting the state
- // left by one, applying a mask to the state, and reducing
- // the result with a bit XOR reduction function.
- // ----- XOR------------> G0
- // | | | |
- // +------------------------------+
- // | b0 b1 b2 b3 b14 b15 | <- in
- // +------------------------------+
- // | | | | |
- // ----- XOR------------> G1
- // Instruction BXOR computes the bit G0 or G1 and stores it into CC
- // and also into a destination reg half. Here, we take CC and rotate it
- // into an output register.
- // However, one can also store the output bit directly by storing
- // the register half where this bit is placed. This would result
- // in an output structure similar to the one in the original function
- // Convolutional_Encode(), where an entire half word holds a bit.
- // The resulting execution speed would be roughly twice as fast,
- // since there is no need to rotate output bit via CC.
- .include "testutils.inc"
- start
- loadsym P0, input;
- loadsym P1, output;
- R1 = 0; R2 = 0;R3 = 0;
- R2.L = 0;
- R2.H = 0xa01d; // polynom 0
- R3.L = 0;
- R3.H = 0x12f4; // polynom 1
- // load and CurrentState to upper half of A0
- A1 = A0 = 0;
- R0 = 0x0000;
- A0.w = R0;
- A0 = A0 << 16;
- // l-loop counter is in P4
- P4 = 2(Z);
- // **** START l-LOOP *****
- l$0:
- // insert 16 bits of input into lower half of A0
- // and advance input pointer
- R0 = W [ P0 ++ ] (Z);
- A0.L = R0.L;
- P5 = 2 (Z);
- LSETUP ( m$0 , m$0end ) LC0 = P5; // **** BEGIN m-LOOP *****
- m$0:
- P5 = 8 (Z);
- LSETUP ( i$1 , i$1end ) LC1 = P5; // **** BEGIN i-LOOP *****
- i$1:
- R4.L = CC = BXORSHIFT( A0 , R2 ); // polynom0 -> CC
- R1 = ROT R1 BY 1; // CC -> R1
- R4.L = CC = BXOR( A0 , R3 ); // polynom1 -> CC
- i$1end:
- R1 = ROT R1 BY 1; // CC -> R1
- // store 16 bits of outdata RL1
- m$0end:
- W [ P1 ++ ] = R1;
- P4 += -1;
- CC = P4 == 0;
- IF !CC JUMP l$0; // **** END l-LOOP *****
- // Check results
- loadsym I2, output;
- R0.L = W [ I2 ++ ]; DBGA ( R0.L , 0x8c62 );
- R0.L = W [ I2 ++ ]; DBGA ( R0.L , 0x262e );
- R0.L = W [ I2 ++ ]; DBGA ( R0.L , 0x5b4d );
- R0.L = W [ I2 ++ ]; DBGA ( R0.L , 0x834f );
- pass
- .data
- input:
- .dw 0x999f
- .dw 0x1999
- output:
- .dw 0x0000
- .dw 0x0000
- .dw 0x0000
- .dw 0x0000
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